1. Technical Field
The present invention embodiments pertain to determining locations of emitters. In particular, the present invention embodiments pertain to determining locations of radio frequency (RF) emitters in a three-dimensional space based on energy or received signal strength (RSS) measurements of the emitters at various locations.
2. Discussion of Related Art
Conventional techniques for geolocation of a radio frequency (RF) emitter are commonly based on measurements of a received signal strength (RSS) of signals transmitted from the emitter. Accordingly, this RSS-based technique may also be referred to as an energy-based technique. The received signal strength (RSS) is usually integrated over the duration of the transmitted signal in order to obtain a signal energy measurement and enhance signal to noise ratio. Since the transmitted radio frequency (RF) signal attenuates during propagation through space, the received signal strength (RSS) of the signal may be used to estimate the distance from the receiver to the emitter. However, this technique may not be very accurate due to multipath fading and shadowing effects that may significantly distort the expected received signal strength (RSS).
In order to improve the accuracy, the received signal strength (RSS) or energy-based geolocation technique may employ a radio frequency (RF) propagation map of the environment. The map is basically a database with information created from known terrain data and learned from observed energy measurements at different combinations of emitter and receiver locations. The improved geolocation technique determines the best fit in the energy space to potential emitter locations based on the radio frequency (RF) propagation map. However, this improved technique requires a large number of real-time measurements and/or terrain modeling. Thus, this technique can only be used in applications in which the radio frequency (RF) propagation map is available, and sufficient computing capacity exists to process the large amount of data.